Vertical Devices Research Articles

Ab Initio Prediction of Ultra‐Wide Band Gap BxAl1−xN Materials

AbstractUltra‐wide bandgap (UWBG) materials are poised to play an important role in the future of power electronics. Devices made from UWBG materials are expected to operate at higher voltages, frequencies, and temperatures than current silicon and silicon‐carbide‐based devices and can even lead to significant miniaturization of such devices. In the UWBG field, aluminum nitride and boron nitride have attracted great interest; however, the BxAl1−xN alloys are much less studied. In this work, using first‐principles simulations combining density‐functional theory and the cluster expansion method, the crystal structure of BxAl1−xN alloys is predicted. Seventeen ground state structures of BxAl1−xN with formation energies between 0.11 and 0.25 eV atom‐1 are found. All of these structures are found to be dynamically stable. The BxAl1−xN structures are found to have predominantly a tetrahedral bonding environment; however, some structures exhibit sp2 bonds similar to hexagonal BN. This work expands knowledge of the structures, energies, and bonding in BxAl1−xN which aids their synthesis, the innovation of lateral or vertical devices, and discovery of compatible dielectric and Ohmic contact materials.

Vertical GaN-on-GaN pn power diodes with Baliga figure of merit of 27 GW/cm2

High power vertical GaN devices are in great demand recently due to their potential on extremely high-power conversion efficiency. Here, we show vertical GaN p–n power diodes fabricated on bulk GaN substrates with an optimized guard ring structure for electrical field management and high breakdown voltage. By using a low doped (∼1015 cm−3) 28 μm thick drift layer in combination with optimized ohmic contacts, a breakdown voltage (VB) of 4.9 kV and a low specific on-resistance (RON) of 0.9 mΩ cm2 were achieved. In combination with the high breakdown voltage and low specific on-resistance, the device demonstrated a Baliga figure of merit (V2B/RON) of 27 GW/cm2.

Enhancement-mode vertical (100) β-Ga2O3 FinFETs with an average breakdown strength of 2.7 MV cm−1

In this work, we report on the realization of vertical (100) β-Ga2O3 FinFET devices for the use in power electronics applications. The experiments are carried out on structures consisting of highly conducting (100) β-Ga2O3 substrates with a doping concentration N D of 3 × 1018 cm−3, and epitaxially grown layers with N D of 5 × 1016 cm−3 for the drift and channel region. The fabricated FinFET devices feature enhancement-mode properties with a threshold voltage of +4.2 V and on/off-current ratio of 105. Moreover, breakdown measurements of these devices reveal an average breakdown strength of 2.7 MV cm−1. Additional device simulation indicates the presence of electric field peaks near the gate edge outside the active device as high as 7 and 5 MV cm−1 in the Al2O3 gate oxide and β-Ga2O3 semiconductor, respectively.

Anisotropy of impact ionization in WSe2 field effect transistors

Carrier multiplication via impact ionization in two-dimensional (2D) layered materials is a very promising process for manufacturing high-performance devices because the multiplication has been reported to overcome thermodynamic conversion limits. Given that 2D layered materials exhibit highly anisotropic transport properties, understanding the directionally-dependent multiplication process is necessary for device applications. In this study, the anisotropy of carrier multiplication in the 2D layered material, WSe2, is investigated. To study the multiplication anisotropy of WSe2, both lateral and vertical WSe2 field effect transistors (FETs) are fabricated and their electrical and transport properties are investigated. We find that the multiplication anisotropy is much bigger than the transport anisotropy, i.e., the critical electric field (ECR) for impact ionization of vertical WSe2 FETs is approximately ten times higher than that of lateral FETs. To understand the experimental results we calculate the average energy of the carriers in the proposed devices under strong electric fields by using the Monte Carlo simulation method. The calculated average energy is strongly dependent on the transport directions and we find that the critical electric field for impact ionization in vertical devices is approximately one order of magnitude larger than that of the lateral devices, consistent with experimental results. Our findings provide new strategies for the future development of low-power electric and photoelectric devices.Graphical

Time–frequency signal analysis of flow pulsation in siphon outlet conduit based on HHT considering the pump‐conduit interaction

AbstractThe unsteady three‐dimensional numerical simulation calculation of the vertical axial flow pump device is performed based on CFD to examine the pressure pulsation and energy distribution features of the water flow within the siphon outlet conduit (SOC) under the hydraulic coupling of the pump and the flow conduit. The pressure pulsation signals (PPS) of monitoring points are decomposed using the Hilbert–Huang approach via empirical mode decomposition (EMD) and Hilbert spectrum analysis. The results show that the PPS of monitoring points of the SOC has no obvious periodicity. The low‐frequency range below 20 Hz serves as the primary frequency, and the energy ratio of the high‐frequency signal above 700 Hz is less than 1%. Under the condition of a small flow rate 0.3Qbep, there is obvious high‐frequency pulsation above 500 Hz at the inlet of the upstream section of the SOC, and there are periodic components distributed around 200 Hz. The energy of the pressure pulsation is primarily focused in the low‐frequency range below 40 Hz at the SOC outlet section. The PPS at the top and bottom monitoring points of the hump section are consistent, and the pressure pulsation energy (PPE) is mainly concentrated in the low frequency below 40 Hz. In both the big flow condition (1.2Qbep) and the optimal flow condition (1.0Qbep), the PPE of the monitoring points at the top of the hump section is distributed in the middle and low‐frequency band below 40 Hz, and the energy of monitoring points at the bottom of the hump section is concentrated in the low‐frequency band below 20 Hz, accounting for more than 70%. When the flow rate increases from 0.3Qbep to 1.2Qbep, the peak value of the pressure pulsation coefficient at the main frequency of each monitoring point at the top of the hump section changes little, and the peak value of the pressure pulsation coefficient at the main frequency of each monitoring point at the bottom increases first and then decreases. From the upstream section to the hump section of the SOC, the average frequency of each intrinsic mode function (IMF) of the PPS under different flow conditions shows an overall increasing trend. From the hump section of the SOC to its outlet, the average frequency of each IMF of the PPS decreases under the conditions of 1.0Qbep and 1.2Qbep, and there is no obvious change under the condition of 0.3Qbep.

Impact of neutron irradiation on electronic carrier transport properties in Ga2O3 and comparison with proton irradiation effects

The minority charge carrier transport in beta gallium oxide (-Ga2O3) before and after exposure to neutrons from a 241Am-Be source was studied. Cathodoluminescence (CL) spectroscopy and current–voltage (I-V) characteristics were used to study minority carrier behavior. High energy radiation affects minority carrier properties through the production of carrier traps that reduce the conductivity and mobility of the material. In this paper, we report the effects of neutron radiation in silicon-doped -Ga2O3, using rectifiers or transistors as the measurement platform. The thermal activation energy of the reference (non-irradiated) sample was 40.9 meV, which is ascribed to silicon-donors. CL measurements indicate a slightly indirect bandgap energy of 4.9 eV. Neutrons create disordered regions in -Ga2O3 rather than just point defects, resulting in the lowest carrier removal rate because of the lowest average non-ionizing energy loss. The neutron irradiation caused an increase in reverse bias leakage current in rectifiers and a carrier removal rate of 480 cm−1 but had little effect on reverse recovery switching time. Differences in CL spectra were observed between vertical and lateral device structures, emphasizing the importance of impurities and defects in the starting material. The neutron energies in the Am-Be source range up to 11 MeV, with an average energy between 4 and 5 MeV (Figure 1). We also contrasted neutron damage with the effects of irradiation with 10 MeV protons. Under 10 MeV proton irradiation, the thermal activation energies increase. This is attributable to high order defects and their influence on carrier lifetimes. The measurements show that -Ga2O3 is more resistant to radiation damage than other wide bandgap semiconductors due to its higher displacement threshold energy, which is inversely proportional to the lattice constant.

Two‐Dimensional Perovskite Single Crystals for High‐Performance X‐ray Imaging and Exploring MeV X‐ray Detection

Scintillation semiconductors play increasingly important medical diagnosis and industrial inspection roles. Recently, two‐dimensional (2D) perovskites have been shown to be promising materials for medical X‐ray imaging, but they are mostly used in low‐energy (≤130 keV) regions. Direct detection of MeV X‐rays, which ensure thorough penetration of the thick shell walls of containers, trucks, and aircraft, is also highly desired in practical industrial applications. Unfortunately, scintillation semiconductors for high‐energy X‐ray detection are currently scarce. Here, This paper reports a 2D (C4H9NH3)2PbBr4 single crystal with outstanding sensitivity and stability toward X‐ray radiation that provides an ultra‐wide detectable X‐ray range of between 8.20 nGyair s−1 (50 keV) and 15.24 mGyair s−1 (9 MeV). The (C4H9NH3)2PbBr4 single‐crystal detector with a vertical structure is used for high‐performance X‐ray imaging, delivering a good spatial resolution of 4.3 lp mm−1 in a plane‐scan imaging system. Low ionic migration in the 2D perovskite enables the vertical device to be operated with hundreds of keV to MeV X‐ray radiation at high bias voltages, leading to a sensitivity of 46.90 μC Gyair−1 cm−2 (−1.16 V μm−1) with 9 MeV X‐ray radiation, demonstrating that 2D perovskites have enormous potential for high‐energy industrial applications.

Nitrogen-doped β-Ga2O3 vertical transistors with a threshold voltage of ≥1.3 V and a channel mobility of 100 cm2 V−1 s−1

We demonstrate high-performance normally-off multi-fin β-Ga2O3 vertical transistors with a wide fin width from 1.0 to 2.0 μm by using a nitrogen-doped β-Ga2O3 high-resistive layer grown by halide vapor phase epitaxy. Normally-off operation was achieved with a threshold voltage of ≥1.3 V, a specific on-resistance of 2.9 mΩ·cm2 and a current density of 760 A cm−2 at a gate voltage of +10 V. The estimated MOS channel field effect mobility was ∼100 cm2 V−1 s−1. These findings offer important insights on the development of Ga2O3 MOSFETs and show the great promise of Ga2O3 vertical power devices.

A Review of Homoepitaxy of III-Nitride Semiconductors by Metal Organic Chemical Vapor Deposition and the Effects on Vertical Devices

This paper reviews some of the basic issues in homoepitaxial growth of III-nitrides to enable a vertical device technology. It focuses on the use of metal organic chemical vapor deposition (MOCVD) to grow GaN and explores the effects of the native substrate characteristics on material quality, interface composition, and device performance. A review of theoretical work understanding dopants in the ultra-wide III-nitride semiconductors, AlN and BN, is also included for future efforts expanding the technology into those materials.

Characterization of unintentional doping in localized epitaxial GaN layers on Si wafers by scanning spreading resistance microscopy

Localized epitaxy of gallium nitride (GaN) on silicon (Si) is studied, with the aim of achieving material compatible with 1200 V vertical devices, in particular an unintentional doping level <1 × 1016 cm−3, which is essential to have high quality devices. In this study, three mask materials (SiN, SiO2, Al2O3) are examined and the unintentional doping concentration in GaN layers grown by metal organic vapor phase epitaxy (MOVPE) is investigated by scanning spreading resistance microscopy (SSRM). The results from SSRM are verified by secondary ions mass spectroscopy (SIMS) and show that an unintentional doping concentration lower than 1016 cm−3 is achieved when Al2O3 is used as the mask material. This value is lower than any previous studies of localized GaN growth, and in addition, this is the first time that SSRM has been used to observe such low doping concentrations in GaN.

Integrated SERS-Vertical Flow Biosensor Enabling Multiplexed Quantitative Profiling of Serological Exosomal Proteins in Patients for Accurate Breast Cancer Subtyping.

Protein profiles of exosomes (EXOs) in clinical samples of cancer patients have become a promising diagnostic and therapeutic biomarker. However, simultaneous quantitative analysis of multiple exosomal proteins of interest remains challenging. To address the unmet need, we develop a paper-based surface-enhanced Raman spectroscopy (SERS)-vertical flow biosensor, named iREX (integrated Raman spectroscopic EXO) biosensor, for multiplexed quantitative profiling of exosomal proteins in clinical serum samples of patients. Utilizing this iREX biosensor, we are able to quantitatively profile MUC1, HER2 and CEA in EXO samples derived from various breast cancer cell subtypes. The results show discriminative expression profiles of the three exosomal proteins in these cell subtypes, which allows for accurate diagnosis and molecular subtyping of breast cancer. We further validate the clinical utility of the iREX biosensor for simultaneous quantitative analysis of MUC1, HER2 and CEA in patient's blood serums, thereby aiding in noninvasive breast cancer subtyping and longitudinal treatment monitoring. Our iREX biosensor integrating the SERS detection in a vertical flow diagnostic device offers great advantages of high sensitivity, molecular specificity, powerful multiplexing capability, and high diagnostic accuracy. We believe that the iREX biosensor could be a promising clinical tool for comprehensive analysis of exosomal proteins in clinical samples for personalized diagnosis and precise management of breast cancer.

Investigation of optimal design damping force based on novel mechanical model for precast wall structures connected by vertical damping devices

Currently, a method for designing the damping force for precast wall structures with vertical damping devices has garnered increasing attention. Therefore, we propose a novel mechanical model for precast walls connected by vertical damping devices based on the continuous link approach and energy principle to compute the optimal design damping force. The proposed model is validated based on experimental data and numerical simulation results obtained using the ABAQUS finite element analysis software. Subsequently, the effect of the aspect ratio of the precast walls on the damping force is analyzed based on the numerical models established. Based on the analysis results, the correlation coefficient between the design and ultimate loads is determined, and a simplified method for computing the optimal design damping force is presented. Finally, the effectiveness of the proposed mechanical model in computing the optimal design damping force is demonstrated via the dynamic time-history analysis of precast wall structures. The efficacy of the proposed mechanical model overcomes the deficiency of the method for designing vertical damping devices, thus providing a foundation for further investigations into structural damage control.

Suppression of particle formation by gas-phase pre-reactions in (100) MOVPE-grown β -Ga2O3 films for vertical device application

This work investigated the metalorganic vapor-phase epitaxy (MOVPE) of (100) β-Ga2O3 films with the aim of meeting the requirements to act as drift layers for high-power electronic devices. A height-adjustable showerhead achieving a close distance to the susceptor (1.5 cm) was demonstrated to be a critical factor in increasing the stability of the Ga wetting layer (or Ga adlayer) on the surface and reducing parasitic particles. A film thickness of up to 3 μm has been achieved while keeping the root mean square below 0.7 nm. Record carrier mobilities of 155 cm2 V−1 s−1 (2.2 μm) and 163 cm2 V−1 s−1 (3 μm) at room temperature were measured for (100) β-Ga2O3 films with carrier concentrations of 5.7 × 1016 and 7.1 × 1016 cm−3, respectively. Analysis of temperature-dependent Hall mobility and carrier concentration data revealed a low background compensating acceptor concentration of 4 × 1015 cm−3.

Solidification time and solid fraction of vertical concentric shell and tube latent heat storage device : A dimensionless parametric study and correlations development

ABSTRACT Thermo-hydraulic behavior of a Phase Change Material (PCM) plays a crucial role in deciding the performance of Latent Heat Storage (LHS) devices. Discharge or Solidification is the prime portion that determines the performance of the LHS device. This work numerically models solidification in a vertical tube-in-tube LHS device. The phase change is accounted for using the fixed grid enthalpy porosity method. An independent numerical model built is validated with the experimental model. Dimensionless parameters, namely Rayleigh Number, Stefan number, Reynolds Number, and L/D ratio, vary in the range of 9.19x105 to 39.45x105, 0.2 to 0.5, 600 to 3000, and 1 to 15, respectively. Among all parameters, the Stefan Number has the greatest impact on the solid fraction and solidification time. For estimating the Solidification Time and Solid Fraction, correlations are proposed.

Understanding the Breakdown Behavior of Ultrawide‐Bandgap Boron Nitride Power Diodes Using Device Modeling

Herein, a device study using technology computer‐aided design simulation to theoretically analyze the electrical performance of ultrawide‐bandgap boron nitride (BN)‐based vertical junction devices is performed, including h‐BN Schottky diode, h‐BN pn diode, and h‐BN/AlN pn diode; this is also the first demonstration of the BN power devices in simulation. The material properties of BN are defined with recently reported data, and the physical mechanisms of the device performance are systematically investigated. The h‐BN junctions in this simulation shows excellent performance, especially for breakdown behaviors. Schottky diode shows a turn‐on voltage of 0.6 V for Pt Schottky contact and breakdown voltages over 450 V for 5 μm, 6 × 1015 cm−3 p‐type‐doped drift layer; The h‐BN pn diode shows a turn‐on voltage of 6 V and breakdown voltages over 3 kV with a critical electric field of 13.6 MV cm−1 for 2.5 μm, 2 × 1016 cm−3 p‐type‐doped drift layer. The h‐BN/AlN heterojunction pn diode shows a turn‐on voltage of 5.8 V and breakdown voltage over 2 kV for 2.5 μm, 2 × 1016 cm−3 n‐type‐doped AlN drift layer. Herein, an understanding of the device principles of vertical BN junctions is provided, which can serve as a reference for the future development of robust BN power electronics.

Prospects for the application of a small wind power device with a vertical axis in the Jizzakh region

In recent years, renewable energy sources, especially wind energy, have been widely used around the world. Big projects are being implemented in Uzbekistan for the development of wind energy in the next decade. Large wind power plants are being built in different regions of the country such as Navoi, Bukhara, and Karakalpakstan. In these wind power plants, horizontal type wind energy devices are mainly used for the production of electricity. Horizontal-axis wind energy devices are used not only in the production of large capacities, but also in providing local consumers with small capacities. However, the share of electricity generation or supply of local consumers with the help of small vertical axis wind energy devices is much smaller. In this article, analyzing the potential of wind energy in Jizzakh region, the prospects of using small vertical wind energy devices are theoretically researched.

An Optimized Vertical GaN Parallel Split Gate Trench MOSFET Device Structure for Improved Switching Performance

This work proposes a vertical gallium nitride (GaN) parallel split gate trench MOSFET (PSGT-MOSFET) device architecture suitable for power conversion applications. Wherein two parallel gates, and a field plate are introduced vertically on the sidewalls and connected, respectively, to the gate and source. Technology computer-aided design (TCAD) simulator was used in the design process to achieve a specific on-resistance as low as 0.79 mΩ.cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the device, which has the capacity of blocking voltages up to 600 V. The peak electric field of the PSGT-MOSFET could well be lowered to 2.95 MV/cm, which is about 17% lower than that of a conventional trench gate MOSFET (TG-MOSFET) near the trench corner with help of suitable design and optimization of trench depth, drift doping, and field plate thickness. The TCAD simulation shows that the higher drift doping on the device performance of PSGT-MOSFET produces ~2× lower switching losses when compared with a similarly rated conventional TG-MOSFET device.

Researching localization of vertical axis wind generators

The paper analyses the economic efficiency of using wind power plants in mountainous areas and small residential areas as well as the results of using vertical axis wind devices in areas with low-speed winds. So it became possible to obtain the necessary electrical energy in the less windy regions of Uzbekistan by using vertical axis wind generators. In recent years the demand for electricity is increasing gradually as a result of the sharp growth of direct production enterprises and population consumption. This demand can be compensated by using not only traditional energy sources but also non-traditional energy sources. The use of wind energy is to a certain extent the basis of energy production. Nurato district of Navoi region of Uzbekistan was selected as an object. The problems of saving and shortage of electric energy will be avoided by using the vertical axis wind generator in the regions. By moving the rotor of the wind generator the wind energy is converted into mechanical energy, which generates electrical energy through the generator. Electric power from the generator is provided by a controller that serves to monitor the charge level of the accumulator and is sent to the accumulator through the controller.

Charge transmission of MoS&lt;sub&gt;2&lt;/sub&gt;/MoTe&lt;sub&gt;2&lt;/sub&gt; vertical heterojunction and its modulation

The heterojunction device based on two-dimensional materials possesses unique photoelectric properties due to its nanoscale thickness and van der Waals (vdWs) contact surface. In this paper, a gate-voltage-tunable MoS&lt;sub&gt;2&lt;/sub&gt;/MoTe&lt;sub&gt;2&lt;/sub&gt; vertical vdWs heterojunction device is constructed. The Kelvin probe force microscopy (KPFM) technology is combined with the electric transport measurement technology, thereby revealing the charge transport behavior of the MoS&lt;sub&gt;2&lt;/sub&gt;/MoTe&lt;sub&gt;2&lt;/sub&gt; heterojunction under dark condition and laser-irradition condition, including the bipolarity characteristics of the transition from n-n&lt;sup&gt;+&lt;/sup&gt; junction to p-n junction. In this paper, the charge transport mechanism of heterojunction is explained comprehensively and systematically, including the charge transmission process of n-n&lt;sup&gt;+&lt;/sup&gt; junction and p-n junction under positive and negative bias conditions, the transformation of nodule behavior with gate voltage, the influence of barriers on charge transmission, the different rectification characteristics between n-n&lt;sup&gt;+&lt;/sup&gt; junction and p-n junction, the major role of source and leakage bias voltage in band tunneling, and the influence of photogenerated carriers on electrical transmission. The method in this work can be generalized to other two-dimensional heterojunction systems and also provide an important reference for improving the performance of two-dimensional semiconductor devices and their applications in the future.

Hydraulic calculation of filtration system in drip irrigation

It is known that water filtration devices are used to increase the efficiency of the drip irrigation system on a large scale. Currently, there are various types of filtering devices, the main purpose of which is to reduce the amount of turbidity in water. In Uzbekistan, vertical and horizontal filters made according to Turkish and Chinese technologies are used. When designing drip irrigation systems, it is necessary to perform a hydraulic calculation. At when performing a hydraulic calculation, it is necessary to calculate the pressure loss in the filtration system and base the pumping unit on this basis. This article presents the results of studies of a vertical filtration device manufactured using Turkish technology. The studies were carried out in natural field conditions, in a filtration system installed in the field of the farm of Ashurov Azizbek Ganievich, located in the Kasbi district of the Kashkadarya region. The filtration system consists of 4 parts and describes studies to determine the coefficient of resistance hydraulic calculation. The studies were conducted in 3 variants. It has been established that the magnitude of pressure losses in the filtration system varies from 2.7 m to 9m. It has been established that the resistance coefficient of the filtration system varies from 61.9 to 247.1 in option 1, from 32.1 to 229.5 in option 2 and from 32.5 to 218.5 in option 3. As a result of the research, a method was developed for determining the resistance coefficient required for the hydraulic calculation of this filter system. A formula for calculating the pressure loss in the filtration room is recommended system.